When Clark University invited Norman Finkelstein to speak, then canceled the speech in response to protesters, Sarah Wunsch of the ACLU wrote:
...the cancellation of his speech violates the basic principles of freedom of speech and academic freedom which are so fundamental to an institute of higher learning. The existence of an opportunity to speak at another time or in another location does not remedy the wrong of censorship.
...Nor may complaints from those disturbed by Finkelstein’s writings about the post-Holocaust “industry” justify a decision to prevent the lecture from taking place. Indeed, even if demonstrators came to protest against Finkelstein’s views, the obligation of a university is to protect the speaker’s right to be heard and prevent disruption of the speech by others. By censoring speech because of complaints about offensiveness or the controversial nature of the speaker, the university has essentially allowed what the courts call a “heckler’s veto” over what speech can be heard.From XKCD doesn't understand free speech—or the difference between legal and moral rights